In the proposed program, the pyruvate dehydrogenase (PDC) and the alpha-ketoglutarate dehydrogenase (KGDC) enzyme complexes are used to study the structural and functional organization of protein molecules in multisubunit assemblies. The two complexes are very similar, each having three kinds of subunits, a dehydrogenase, a lipoyl containing core enzyme, and a flavoprotein. The goal of the research is to determine the arrangement of subunits in the complexes and to therefore understand the coordinated sequence of reactions catalyzed by the complex. A three part program is proposed. Part one consists of an 8 angstrom units X-ray diffraction analysis of crystals of lipoyl transsuccinylase (LTS), the core of the KGDC complex. The technique of multiple isomorphous replacement will be used. The resulting map will show the features of and internal arrangement of matter in the core. Part two consists of a combined X-ray diffraction and electron microscopic study on noncrystalline preparations of both complexes and their component parts. The high symmetries of the complexes make possible the interpretation both of the solution scattering patterns and electron micrographs in terms of an arrangement of subunits in the two complexes. Valuable inferences may result from comparison of the two complexes and from comparison of the enzymes prepared from mammalian tissues with those prepared from bacteria. In part three, the eight types of crystals which have been found so far will be examined by electron microscopy and/or X-ray diffraction.